1. Field of the Invention
The present invention relates to a directional valve of the type suitable for use in a breathing apparatus, the directional valve having a valve seat with a valve port and a valve plate resting loosely on the valve seat.
2. Description of the Prior Art
Directional valves are used in breathing apparatuses for e.g. controlling flow to and from the user of the apparatus (usually a patient) to prevent or minimize re-breathing of expired gas.
Special demands are made on these directional valves in anaesthetic machines. The valve must seal over a wide dynamic counter-pressure range, typically from 1-2 mbar up to 200 mbar. At the same time, it must open to allow the passage of a flow at low pressure differences, typically a few mbar. This corresponds to a total force of a few tenths of a newton on the valve plate. Valve opening must be as independent of moisture (present at high levels in anaesthetic machines) as possible.
The valve""s components also must be capable of withstanding an aggressive environment (anaesthetic gases and autoclaving) and feature an environmentally and economically advantageous design.
An object of the present invention is to provide a directional valve which satisfies the aforementioned demands.
The above object is achieved in accordance with the principles of the present invention in a directional valve for a breathing apparatus having a valve seat with a valve port and a valve plate resting loosely on the valve seat, the valve plate having a soft, pliable area on its surface in contact with the valve seat, and a relatively stiff area extending across the valve port.
By using a valve plate with a soft and pliable area in contact with the valve seat, the latter can be devised with less surface precision. As a result, more economical materials and fabrication procedures, such as injection molded plastic, can be used. The stiffer area across the valve port keeps the valve plate from being drawn or forced down into the valve port when large pressure differences prevail.
As the description above indicates, the valve plate must be very light. This is achieved in an embodiment wherein the valve plate is a membrane, with a thin, soft outer edge, whose thickness increases in toward the center of the membrane.
Alternatively, the valve plate can be a thin, soft membrane on which a rigid plate is attached to provide stiffness. The plate should not be too heavy.